Although applicable to a number of fields, the present invention relates primarily to hydraulic oil filters. Filters have long been used in hydraulic systems to remove contaminants from hydraulic oil. It is well known that, with time, hydraulic oil filters become plugged or clogged with contaminants and are required to be replaced.
A typical hydraulic filter assembly includes a housing (e.g., a bowl or canister) containing a cylindrical filter element. The cylindrical filter element typically defines a central longitudinal opening in which a central core is mounted. The core provides support for preventing the filter element from collapsing inward. In use, oil is directed from a hydraulic system into an annular channel defined between the housing and the outer surface of the filter element. Pressure from the hydraulic system forces the hydraulic oil from the annular flow passage, through the filter element, and into the central opening of the filter element. From the central opening of the filter element, the filtered hydraulic oil is discharged from the filter assembly.
Disposable or "throw-away" type fluid filters are well known in the art. In this type of filter assembly, the filter element is permanently sealed within the housing. When the filter element becomes clogged with contaminants, the entire filter assembly is discarded and replaced with a new unit.
Oil filter assemblies having replaceable filter elements are also known in the art. Filter assemblies with replaceable filter elements are desirable because the housing can be reused thereby reducing the amount of waste that enters the waste stream. Consequently, as landfill costs increase, filter assemblies having replaceable filter elements will become increasingly more desirable.
Contamination is an important consideration relating to filter assemblies having replaceable filter elements. For example, prior art systems having replaceable filter elements can experience the accumulation of contaminants within the reusable housings that cover the replaceable filter elements. If this occurs, the "clean" side of new filter elements inserted within the contaminated housings can immediately become contaminated. There is a need in the art to prevent this type of contamination from occurring.